The problem, imo, is with half-assing it. Tip jars are doomed to fail from what I've seen second hand, and all they do is make you feel bad/like a failure. If you want to give yourself a financial incentive to write, you have to give your readers a serious (but also reliable) incentive to support you financially. Just saying "feel free to donate but all content will remain free" is going to result in nobody donating.